Project Summary/Abstract Vascular smooth muscle cells (VSMCs) support the formation, structural integrity and chemical responsivity required for development, post-natal maturation and function of the blood vasculature. Following the process of vasculogenesis wherein endothelial cells (ECs) coalesce to form a primitive, tubular capillary network, recruitment of VSMCs promotes vessel maturation or angiogenic remodeling governed by a complex interplay of signaling and transcriptional programs operating within ECs and VSMCs. The balance of these activities critically regulates vascular formation and function under physiologic and pathologic conditions. Previous studies published by the PI revealed that suppression of canonical Notch signaling in VSMCs in vivo resulted in improper cerebral arterial patterning as well as failure to form mature arterial vessel walls. These findings identified a VSMC-autonomous role for Notch signaling in the formation of competent vessels and implicated an important role for Notch signaling in arterial patterning and collateral artery formation. In addition, these anatomical derangements were associated with an increased risk for cerebrovascular insufficiency and stroke in mice subjected to induced ischemia. Taken together, these observations support our central hypothesis that Notch signaling in VSMCs provides instructive cues required for proper organization and function of the arterial vasculature. The goal of this proposal is to further study, in a comprehensive manner, the role of Notch signaling in VSMC biology in vitro and in vivo. In Aim 1, studies in mouse embryos harboring Notch signaling-deficient VSMCs will be undertaken to map the temporal-spatial organization of emerging vessels during pre-natal development as a basis for the observed post-natal anatomical abnormalities. Aim 2 will address the functional dynamics of Notch signaling-deficient VSMCs within native vessels by examining vasoreactive responses to physiological and chemical stimuli important for cerebral and peripheral vascular homeostasis. Finally, Aim 3 will examine the molecular basis for altered vessel structure and VSMC function in part through ex vivo and in vitro studies assessing the angiogenic and vessel remodeling contributions of Notch signaling-deficient VSMCs.